The circuitry used for computing systems has advanced at a rapid rate. Circuit elements for both logical circuitry and memory circuitry, such as magnetic random access memories (MRAM), have steadily shrunk and, in many cases, required ever decreasing amounts of power to operate. However, the ever increasing demands for yet faster processing, greater storage capacity, and lower power consumption continues to require new developments for the circuitry and circuit elements used in memory and processing circuitry.
One example of the past years' advancements in computer circuitry are read heads or field sensors that take advantage of the tunneling magnetoresistance (TMR) effect. In a typical TMR-type structure, two magnetic layers are separate by an ultra thin insulating barrier material, such as Al2O3. When driving an electric current through such a tri-layer system, the resistance of the system depends on the relative orientation of the magnetization in the two magnetic layers. The magnetic orientation of the sensor layer may rotate in accordance with the stray field created by a magnetic bit of MRAM, while the pinned magnetization of the second layer remains constant in magnitude and direction. The combination of these two layers, in turn, provide the read head functionality of the device, as the varying electrical resistance across the device will indicate whether the magnetic fields of the two layers are aligned or unaligned, which depends upon the magnetic properties of the magnetic bit being read. Similarly, the TMR effect in multi-layer structures may be used in the development and fabrication of MRAM itself. In MRAM, one bit of information may be encoded in the relative orientation of a top magnetic layer relative to a pinned bottom layer. The magnetization state of the top layer may be set via the magnetic stray-field of a writing current. The information written in this manner may subsequently be read by driving a current through the structure and, based upon the observed resistance, determining whether the magnetic orientations of the two layers are aligned or unaligned, which may correspond to either a one or a zero.